[Measurement of alveolar bone thickness of adult skeletal Class III patients in mandibular anterior region].

Purpose: To describe alveolar bone thickness in mandibular anterior region of skeletal Class III malocclusion with the help of Cone-beam CT.

Methods: The subjects were selected from consecutive adult patients seeking orthodontic treatment in Shanghai Ninth People's Hospital Affiliated to Shanghai Jiao Tong University School of Medicine from January 2008 to March 2011, which included 64 patients diagnosed to be skeletal Class I malocclusion (Class I group) and 66 patients diagnosed to be skeletal Class III malocclusion (Class III group). Both Class I and Class III groups were divided into 3 divisions respectively according to different vertical facial types. Mandibular left central incisor of each subject was chosen for measurement. The labial (L1), lingual (L2) and total (L0)alveolar bone thickness of skeletal Class III patients in mandibular anterior region were assessed using a CBCT analyzing method with Class I group as the control group. Data was processed with SAS8.02 software package.

Results: L1(P<0.05),L2(P<0.01) and L0(P<0.01) of Class III group were thinner than those of Class I group. L1 of high-angle Class III malocclusion was thinner than that of average-angle(P<0.01)and low-angle(P<0.01) ones ; L2 of average-angle Class III malocclusion was thinner than that of low-angle ones(P<0.01) and thicker than that of high-angle ones(P<0.05); L0 of low-angle Class III malocclusion was thicker than that of average-angle ones(P<0.01),which was thicker than that of high-angle ones(P<0.01). L1 of Class III group with different vertical facial types was thicker than L2(P<0.01).

Conclusions: Skeletal Class III malocclusion exhibits thinner alveolus around the mandibular incisor apices compared with Class I malocclusion, which shows strong connection with different vertical facial types. Root apices of mandibular anterior teeth of skeletal Class III malocclusion situated closer to labial cortical bone than lingual cortical bone. It is necessary to access the alveolar bone thickness of adult skeletal Class III patients in mandibular anterior region before orthodontic camouflage or surgical-orthodontic treatment. Orthodontic camouflage might not be a reasonable treatment alternative for these patients.